The present invention relates to guides, or pilots, to position a screw or drill bit in the center of a countersink hole and more particularly to one of the type that is of frangible material that is broken and removed after the guiding function has been completed.
One type of operation that is regularly performed in woodworking operations is to provide an entry point for a screw or drill bit that is centered in a hole that is countersunk in a member. A countersink hole is one that is at the termination of a wall that tapers downwardly from the member surface. The screw or drill bit is to be inserted through the hole to engage a wood piece on which the member lies and to which it is to be fastened. For example, a typical leaf type hinge has three or more countersink holes on each leaf. A wood screw is to be inserted into each countersink hole and the screw head is recessed in the countersink.
When inserting a screw into the wood piece through a countersink hole, it is necessary that the tip of the screw be precisely centered in the hole. Most often the screw tip is inserted directly into the wood piece but sometime the tip of the screw is placed in a pilot hole that has been drilled in the wood piece. In either case the screw tip or the drill bit that makes the pilot hole must be precisely centered in the hole. Otherwise, when the screw is screwed down, the screw head will not be fully recessed in the countersink. This can also cause misalignment of the hinge.
Accordingly, a need exists to provide a simple and inexpensive device to directly center the point of entry of a screw or drill bit in a countersink hole into the wood piece.
In one embodiment of the invention a guide is provided to center the point of entry of a screw tip or drill bit into a wood piece through a hole of a countersink in a member. The guide has a bottom end that is tapered to generally correspond to the countersink and rests on the tapered wall of the countersink that surrounds the hole. The guide has a passage through which the screw or drill bit extends to engage the wood piece. The matching tapers of the guide and the countersink wall centers the screw tip in the hole so that it can be accurately centered to engage the wood piece.
In a preferred embodiment the guide is made of frangible plastic material and houses a screw. As the screw is threaded into the wood it fractures the guide which breaks into pieces that can be removed. In one use of this embodiment, a leaf type hinge can be sold with a set of screws each having the attached guide. This provides a convenience feature for the person attaching the hinge at very little cost.
In a modification of this embodiment, the frangible guide can be provided with one of a surrounding flange or extending lugs spaced around the guide. The flange rests on the surface of the member in which the countersink is formed and the lugs fit into corresponding grooves that are formed in the member. The guide tapered bottom end centers the guide in the countersink and the flange or lugs stabilizes the guide so that the screw will enter the wood at a perpendicular orientation. If desired, there can be an adhesive on the lower face of the flange that engages the hinge leaf.
In another embodiment of the invention, the guide is inserted in the countersink hole and held in position by a locking ring acting against the underside of the member with the countersink or by an adhesive. In a first form the guide is for a drill bit which passes into the hole in the guide to engage the wood piece to make the pilot hole. The drill bit is withdrawn and the guide is pried out of the countersink hole. In a modification of the foregoing for guiding insertion of a screw, the guide is made in two pieces and after the screw tip passes through the guide central hole into the wood piece, the two pieces of the guide are removed from the countersink hole.
An object of the invention is provide a guide to directly center the point of entry of a screw or drill bit tip in a countersink hole in a member into the wood piece under the member.
A further object is to provide a guide for centering a drill bit in a countersink hole of a member to drill a pilot hole in a wood piece under the member.
Another object is to provide a frangible guide holding a screw that centers its tip in a countersink hole.
Yet another object is to provide a guide for use with a member having a countersink hole to center the tip end of a screw or dill bit in the hole.
An additional object is to provide an insert to guide a drill bit or screw that is located in a countersink and attached to the member having the countersink by an adhesive.